The Food and Drug Administration (FDA or Agency) is announcing the availability of a final guidance for industry entitled “Severely Debilitating or Life-Threatening Hematologic Disorders: Nonclinical Development of Pharmaceuticals.” This guidance outlines nonclinical studies recommended for the development of pharmaceuticals used to treat patients with severely debilitating or life-threatening hematologic disorders (SDLTHDs) and addresses comments received to the docket. This guidance is intended to streamline the development of pharmaceuticals used to treat patients with SDLTHDs, other than cancer, while protecting patients' safety and avoiding unnecessary use of animals, in accordance with the 3R (reduce, refine, replace) principles. This guidance applies to pharmaceuticals used both to treat the active disease and to prevent the recurrence of a life-threatening or debilitating event.